A microwave heating apparatus of this kind is generally constituted to include a heating chamber containing an object to be heated, a magnetron for oscillating a microwave, an electricity feeding port formed at a wall face of the heating chamber from which the microwave is radiated into the heating chamber, a waveguide for guiding the microwave to the electricity feeding port. A position of arranging the electricity feeding port and a mode of the electricity feeding port are devised in order to prevent an unevenness in heating from being brought about by reducing a deviation in an electric field intensity distribution at inside of the heating chamber.
As a position of arranging the electricity feeding port, any of inner wall faces partitioning the heating chamber is selectable and heretofore, there have been proposed various constitutions of a constitution of providing the electricity feeding port at a side wall of the heating chamber, a constitution of providing the electricity feeding port at a bottom wall of the heating chamber, a constitution of providing the electricity feeding port at a ceiling wall of the heating chamber and so on.
Further, generally, it is difficult to resolve the deviation in the electric field intensity distribution at inside of the heating chamber by simply providing the electricity feeding port and in order to resolve occurrence of the unevenness in heating caused by the deviation in the electric intensity distribution, it is dispensable to mount rotating means (stirrer) for stirring the microwave or a turntable for turning the object at inside of the heating chamber and by mounting these, the apparatus tends to be large-sized.
In a market of the microwave heating apparatus in recent times, small-sized formation is required. Hence, there has been intensively carried out a research of achieving small-sized formation by omitting to mount the stirrer or the turntable by arranging the electricity feeding port at the ceiling wall of the heating chamber.
FIG. 7 shows a microwave heating apparatus of a background art arranged with an electricity feeding port constituting a port of radiating a microwave at a ceiling wall of heating chamber (refer to, for example, JP-A-57-103292).
FIG. 7 is a sectional view viewing a microwave heating apparatus 1 disclosed in JP-A-57-103292 as mentioned above, from a front side, and the microwave heating apparatus 1 is constituted to include an external cabinet 3, a heating chamber 5 for containing an object such as food or the like to be heated, a magnetron 7 for oscillating a microwave, an electricity feeding port 9 formed at a ceiling wall 11 of the heating chamber 5 from which a microwave is radiated into the heating chamber 5, and a waveguide 13 for guiding the microwave oscillated from an antenna 12 of the magnetron 7 to the electricity feeding port 9.
The magnetron 7 is arranged on a right outer side of the heating chamber 5 and attached to a base end of the waveguide 13 in an attitude of directing the antenna 12 upwardly.
The illustrated waveguide 13 is constituted by a shape of a straight pipe having a rectangular section and is provided with a length from a surrounding of the antenna 12 to the electricity feeding port 9.
Meanwhile, when a wave length of the microwave propagated at inside of the wave guide 13 is designated by notation λg, in order to efficiently radiating the microwave from the electricity feeding port 9, with regard to a length in an axial direction of the wave guide 13, it is preferable to constitute a distance between the antenna 12 of the magnetron 7 and a center of the electricity feeding port 9 by λg/2 multiplied by an integer. Further, in order to restrain a deviation in an electric field intensity distribution bringing about a nonuniformity in heating, it is preferable to make the electricity feeding port as proximate to a center of the heating chamber as possible.
However, according to the wave guide 13 in the shape of the straight pipe as shown by FIG. 7, in the case in which a width dimension of the heating chamber 5 is designated by notation W1, and a distance from a right side wall 15 of the heating chamber 5 to the center of the electricity feeding port 9 is designated by notation L1, when with regard to the length in the axial direction of the wave guide 13, the distance between the antenna 12 and the center of the electricity feeding port 9 is constituted by 3/2 λg, a clearance is produced between the magnetron 7 and the right side wall 15.
The clearance becomes a wasteful space and therefore, although various methods have been adopted in order to prevent the wasteful space, first, when the magnetron 7 is shifted to a left side of the drawing, the distance between the antenna 12 and the center of the electricity feeding port 9 is shifted from λg/2 multiplied by an integer.
Second, when the magnetron 7 and the wave guide 13 and the electricity feeding port 9 are simultaneously shifted to the left side of the drawing, the electricity feeding port 9 is shifted from the center of the heating chamber 5.
Third, when the right side wall 15 of the heating chamber 5 is shifted to a right side of the drawing, the electricity feeding port 9 is similarly shifted from the center of the heating chamber 5.
Fourth, although it is conceivable to shift a left side wall of the heating chamber 5 to the left side simultaneous with the third method, in such a method, the width dimension W1 of the heating chamber 5 is increased.
Further, a height of the wave guide 13 needs to be equal to or larger than a length of the antenna 12 and there also poses a problem that an increase in a height dimension H1 of the wave guide 13 gives rise to an increase in the dimension in a height direction of the apparatus.
The invention has been carried out in view of the above-described problem and it is an object thereof to provide a microwave heating apparatus capable of restraining a deviation in an electric field intensity distribution causing to bring about a nonuniformity in heating by eliminating a wasteful space between a magnetron and an outer side face of a heating chamber and setting an electricity feeding port at a center in a width direction of the heating chamber even when a distance between an antenna and a center of the electricity feeding port is set to a half of a wave length of a microwave at inside of a wave guide multiplied by an integer with regard to a length in an axial direction of the wave guide, capable of shortening a height dimension of the apparatus by contracting a height dimension of the wave guide along a direction of projecting an antenna of the magnetron and capable of realizing small-sized formation of the apparatus while restraining the nonuniformity in heating caused by a deviation in a position of mounting the electricity feeding port from being brought about.